2.1.2 Protocol Relationships

The following figure shows the protocol layering
relationships for the Content Caching and Retrieval member protocols. The
default relationship, which is indicated by a solid arrow, is "is
transported by". The "includes" notation means that a protocol
document includes a second document by reference (for example, [MS-SMB2]
includes [MS-FSCC]).
Member protocols are shown in shaded boxes.

Content Caching and Retrieval can be initiated both by SMB2
and HTTP. A Background Intelligent Transfer Service (BITS) client can use the
system and acts as an HTTP client.

A content
client can use either HTTP or HTTPS for communication with a hosted cache server
specifically while it offers content.<4> The content
is then retrieved by using the Peer Content Caching and Retrieval: Retrieval
Protocol, as described in [MS-PCCRR].

A content client uses the Peer Content Caching and Retrieval
Discovery Protocol, as described in [MS-PCCRD]
(an implementation of [WS-Discovery]),
to locate peer computers
with cached content.

The majority of traffic in the system is performed by the
Peer Content Caching and Retrieval: Retrieval Protocol, as described in
[MS-PCCRR]. This protocol is used to transfer actual content regardless of the
protocol that retrieved the content metadata.